Turbine driveshaft for ram air turbine

ABSTRACT

A driveshaft for an aircraft ram air turbine includes a tubular body and a flange. The tubular body defines an axis of rotation and includes a forward portion and a frusto-conical portion located rearward of the forward portion. The flange adjoins the forward portion of the tubular body opposite the frusto-conical portion, and has a forward face and an opposite rear face. A ratio of an outer diameter of the forward portion of the tubular body to an inner diameter of the forward portion of the tubular body is in a range of approximately 1.423 to 1.425.

BACKGROUND

The present invention relates generally to driveshafts and theirmanufacture, and more particularly to driveshafts for use in housingsand/or gearboxes of ram air turbines (RATs) and their method ofmanufacture.

RATs are used on aircraft to provide an emergency power supply to powera generator, hydraulic pump, etc. When not in use, the RAT is generallystowed within the aircraft fuselage. When the aircraft is in flight, theRAT can be deployed to generate power as turbine blades of the RAT spinin oncoming airflow around the aircraft. The RAT can be deployed as asecondary or emergency system when power is unavailable from primarysystems of the aircraft.

Driveshafts used in RAT drivetrains are subject to many requirements.The RAT driveshaft must be reliable and it must be able to mate withnecessary drivetrain components and be able handle the torque loads towhich it will be subjected. Due to the fact that most RATs protrudeoutward from an aircraft's fuselage in a cantilevered manner, RATs andtheir subcomponents are subject to a significant amount of vibration andbending. Moreover, the rotational nature of RAT drivetrains canintroduce torsional resonance issues. However, because positioning ofthe RAT in the aircraft must account for numerous other aircraft designfactors, the location of the RAT and its subcomponents is highlyconstrained, which greatly limits design options for the geometry anddimensions of the RAT drivetrain and its driveshafts. Weight of RATcomponents is also an important design consideration.

SUMMARY

A driveshaft for an aircraft ram air turbine according to the presentinvention includes a tubular body and a flange. The tubular body definesan axis of rotation and includes a forward portion and a frusto-conicalportion located rearward of the forward portion. The flange adjoins theforward portion of the tubular body opposite the frusto-conical portion,and has a forward face and an opposite rear face. A ratio of an outerdiameter of the forward portion of the tubular body to an inner diameterof the forward portion of the tubular body is in a range ofapproximately 1.423 to 1.425.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a ram air turbine (RAT) according tothe present invention.

FIG. 2 is an enlarged perspective view of a portion of the RAT of FIG.1.

FIG. 3 is a cross-sectional view of the portion of the RAT of FIG. 2,taken along line 3-3 of FIG. 2.

While the above-identified drawing figures set forth embodiments of theinvention, other embodiments are also contemplated, as noted in thediscussion. In all cases, this disclosure presents the invention by wayof representation and not limitation. It should be understood thatnumerous other modifications and embodiments can be devised by thoseskilled in the art, which fall within the scope and spirit of theprinciples of the invention. The figures may not be drawn to scale Likereference numbers have been used throughout the figures to denote likeparts.

DETAILED DESCRIPTION

FIG. 1 is a cross-sectional view of a ram air turbine (RAT) 10 for usewith an aircraft (not shown). For simplicity, FIG. 1 is shown withoutcross-hatching. The RAT 10 includes a turbine assembly 12, a strut 14, agenerator 16, and a drivetrain (or driveline) 18 that includes a strutdriveshaft 20 and turbine driveshaft 22. The strut 14 providesstructural support of the RAT 10 and helps support the turbine assembly12. In the illustrated embodiment, the strut 14 has a hollow andgenerally cylindrical shape. Moreover, in the illustrated embodiment,the generator 16 is positioned at a proximal end of the strut oppositethe turbine gearbox assembly 12. It should be noted that the generator16 is merely one form of power conversion device that can be used withthe RAT 10, and is shown merely by way of example and not limitation.For instance, a hydraulic pump can be used in place of or in addition tothe generator 16 in further embodiments. The drivetrain 18 includessuitable shafts and gearing to provide a mechanical connection betweenthe turbine assembly 12 and the generator 16, in order to transmitrotational energy (torque) to the generator 16, as explained furtherbelow.

In the illustrated embodiment, the turbine assembly 12 includes turbineblades 24, a hub 26, and a locking mechanism 28. The turbine assembly 12can further include additional components as desired, such as suitablepitch or speed control mechanisms located within the hub 26. The turbineblades 24 are secured to the hub 26, and can have adjustable pitch insome embodiments. During operation, the turbine blades 24 can interactwith airflows to produce rotation of the hub 26. In one embodiment, theturbine assembly 12 is configured to have an operating range ofapproximately 3,800-5,000 RPM (or 63.33-83.33 Hz).

The hub 26 is secured to the turbine driveshaft 22, which rotates at thesame speed as the hub 26. The turbine driveshaft 22 is part of thedrivetrain 18 and extends into a gearbox 30, which can be located aft ofthe hub 16 and the turbine blades 24. The gearbox 30 can be secured toand supported by a distal end of the strut 14. The gearbox 30 containssuitable gearing of the drivetrain 18 to provide a gear ratio to operatethe strut driveshaft 20. The locking mechanism 28 can be configured toselectively insert a plunger into a mating feature (e.g., opening) inthe turbine driveshaft 22 to selectively stop rotation of the turbinedriveshaft 22, the hub 26, and other components engaged therewith.

The strut driveshaft 20 is part of the drivetrain 18, and is positionedat least partially within the strut 14. The strut driveshaft 20 candirectly engage the generator 16.

The RAT 10, in the illustrated embodiment, is configured to beselectively deployable from fuselage of the aircraft using suitableactuators (not shown). When deployed, the RAT 10 presents the turbineassembly 12 to airflow passing the aircraft, and can be used to generatedesired forms of power using kinetic energy from rotation of componentsof the turbine assembly 12 produced by the passing airflow. The RAT 10can be deployed in-flight to provide emergency or secondary power.Because the general configuration and use of RATs is well known, furtherdiscussion here is unnecessary.

FIG. 2 is an enlarged perspective view of a portion of the RAT 10, andFIG. 3 is a cross-sectional view of the portion of the RAT 10, takenalong line 3-3 of FIG. 2. As shown in the illustrated embodiment, thestrut driveshaft 20 extends into the gearbox 30 and is rotatablysupported relative to the gearbox 30 by two bearing sets 32. A piniongear 34 is attached to a distal end of the strut driveshaft 20, and canbe positioned in between the bearing sets 32.

In the illustrated embodiment, the turbine driveshaft 22 extends throughthe gearbox 30, and is rotatably supported relative to the gearbox 30 bytwo bearing sets 36. A ring gear 38 is attached to the turbinedriveshaft 22, and meshes with the pinion gear 34 to transmit powerbetween the turbine driveshaft 22 and the strut driveshaft 20 at adesired gear ratio. Splines 40 can be provided in the turbine driveshaft22 to form a “back drive” connection for external tooling to be attachedto the RAT 10 to rotate the drivetrain 18 for maintenance and safetyinspection purposes. A pair of diametrically opposed openings 42 can beprovided in the turbine driveshaft 22 to allow engagement with a lockingmember (e.g., plunger or pin) of the locking mechanism 28.

The turbine driveshaft 22 includes a flange 50 that can interface withthe hub 26. The flange 50 can be secured to the hub 26 with suitablebolts at or near a perimeter of the flange 50. The flange 50 has aforward face (to the left in FIG. 3) that can be arranged at an angle ofapproximately2° (+/−0.25°) relative to an axis of rotation A, and has arear face (to the right in FIG. 3) that can be arranged at approximately9° (+/−0.25°). In this way the flange 50 can taper from a thicker innerdiameter portion to a thinner outer diameter portion. The inner diameterportion of the flange 50 at a base of the taper can have a wallthickness of approximately 2.240 cm (0.882 inches). Extending rearwardfrom the flange 50 of the turbine driveshaft 22 is a body portion thatis tubular in shape with a hollow interior cavity. An axial length L ofthe body portion of the turbine driveshaft 22 can be approximately22.715 cm (8.943 inches). The tubular body portion of the turbinedriveshaft 22 can include a frusto-conical portion 54 (also called theshaft cone), which can be located approximately 6.78 cm (2.67 inches)rearward from the flange 50, with the turbine driveshaft 22 beingsubstantially cylindrical in shape between the flange 50 and thefrusto-conical portion 54. The frusto-conical portion 54 creates spaceto accommodate one of the bearing sets 32 and the distal end of thestrut driveshaft 20. The frusto-conical portion 54 can be arranged atapproximately 14° (+/−0.5°) relative to the axis A. A hub pilot diameterØ1 can be defined adjacent to the forward face of the flange 50, and canbe approximately 18.001 cm (7.090 inches). An outer diameter Ø2 of thebody of the turbine driveshaft 22 at the forward bearing set 36 can beapproximately 7.117 cm (2.802 inches) and a corresponding inner diameterØ3 can be approximately 4.994 cm (1.966 inches), resulting in acorresponding wall thickness of approximately 2.123 cm (0.836 inches).

In one embodiment, a ratio of the outer diameter Ø2 of the body of theturbine driveshaft 22 to the corresponding inner diameter Ø3 can be inthe range of approximately 1.423 to 1.425. In one embodiment, a ratio ofthe outer diameter Ø2 of the body of the turbine driveshaft 22 to thehub pilot diameter Ø1 can be in the range of approximately 1.359 to1.380. Further, in one embodiment, a ratio of the inner diameter Ø3 ofthe body of the turbine driveshaft 22 to the hub pilot diameter Ø1 canbe in the range of approximately 0.954 to 0.968.

Certain dimensions of the turbine driveshaft 22 are critical toperformance. In addition to the angles of the front and rear faces ofthe flange 50 mentioned above, thicknesses of particular portions of theturbine driveshaft are significant. Ratios of the various dimensionsdiscussed above can also be significant. Together, the combination ofthese design parameters of the turbine driveshaft 22 produces desirablevibration performance.

During operation, the RAT 10 is subject to various forces, includingtorques, vibration and bending. The turbine driveshaft 22, inparticular, must be able to transmit suitable torque loads, and musthave geometry and size characteristics that allow portions of it to fitwithin the gearbox 30 and engage with other components of the RAT 10.For instance, the turbine driveshaft 22 should be able to interface withexisting hubs 26 and interface with the locking mechanism 28. Becausethe turbine assembly 12 is subject to a variety of forces duringoperation, bending moments can be imparted to the turbine driveshaft 22.It has been discovered that lateral movement of the turbine driveshaft22 in a direction in and out of the page as shown in FIG. 3 can causedisplacement between the pinion gear 34 and the ring gear 38, whichleads to torque ripples through the drivetrain 18. Torque ripple is anincrease and decrease in torque transmission over time. The harmonicresponse characteristics of the RAT can cause amplified lateral movmentof the turbine driveshaft through twisting of the RAT strut. Byincreasing the lateral stiffness of the turbine driveshaft 22, theselarge amplifications can be moved outside of the operating range of theRAT and subsequently torque ripple can be reduced.

Any relative terms or terms of degree that used herein, such as“substantially”, “approximately”, “about”, “essentially”, “generally”and the like, should be interpreted in accordance with and subject toany applicable definitions or limits expressly stated herein. In allinstances, any relative terms or terms of degree used herein should beinterpreted to broadly encompass any relevant disclosed embodiments aswell as such ranges or variations as would be understood by a person ofordinary skill in the art in view of the entirety of the presentdisclosure, such as to encompass ordinary manufacturing tolerancevariations and the like.

While the invention has been described with reference to an exemplaryembodiment(s), it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment(s) disclosed, but that theinvention will include all embodiments falling within the scope of theappended claims.

1. A driveshaft for an aircraft ram air turbine, the driveshaftcomprising: a tubular body that defines an axis of rotation and thatincludes a forward portion and a frusto-conical portion located rearwardof the forward portion; and a flange adjoining the forward portion ofthe tubular body opposite the frusto-conical portion, the flange havinga forward face and an opposite rear face, wherein a ratio of an outerdiameter of the forward portion of the tubular body to an inner diameterof the forward portion of the tubular body is in a range ofapproximately 1.423 to 1.425.
 2. The driveshaft of claim 1 and furthercomprising: a hub pilot located adjacent to the forward face of theflange, wherein a ratio of the outer diameter of the forward portion ofthe tubular body to the hub pilot diameter is in the range ofapproximately 1.359 to 1.380.
 3. The driveshaft of claim 1, wherein alength of the tubular body, measured in an axial direction, isapproximately 22.715 cm (8.943 inches).
 4. The driveshaft of claim 1,wherein the frusto-conical portion is arranged at approximately 14° withrespect to the axis.
 5. The driveshaft of claim 1, wherein the forwardface of the flange is arranged at approximately 2° with respect to theaxis, and wherein the rear face of the flange is arranged atapproximately 9° with respect to the axis.
 6. The driveshaft of claim 1and further comprising: a hub pilot located adjacent to the forward faceof the flange, wherein the hub pilot has a diameter of approximately18.001 cm (7.090 inches), wherein a length of the tubular body, measuredin an axial direction, is approximately 22.715 cm (8.943 inches),wherein the frusto-conical portion is arranged at approximately 14° withrespect to the axis, wherein the forward face of the flange is arrangedat approximately 2° with respect to the axis, and wherein the rear faceof the flange is arranged at approximately 9° with respect to the axis.7. A driveshaft for an aircraft ram air turbine, the driveshaftcomprising: a tubular body that defines an axis of rotation and thatincludes a forward portion and a frusto-conical portion located rearwardof the forward portion; and a flange adjoining the forward portion ofthe tubular body opposite the frusto-conical portion, the flange havinga forward face and an opposite rear face, wherein the frusto-conicalportion is arranged at approximately 14° with respect to the axis, andwherein the rear face of the flange is arranged at approximately 9° withrespect to the axis.
 8. The driveshaft of claim 7, wherein the forwardface of the flange is arranged at approximately 2° with respect to theaxis.
 9. The driveshaft of claim 7, wherein an outer diameter of theforward portion of the tubular body is approximately 7.117 cm (2.802inches) and an inner diameter of the forward portion of the tubular bodyis approximately 4.994 cm (1.966 inches).
 10. The driveshaft of claim 7and further comprising: a hub pilot located adjacent to the forward faceof the flange, wherein the hub pilot has a diameter of approximately18.001 cm (7.090 inches).
 11. The driveshaft of claim 7, wherein alength of the tubular body, measured in an axial direction, isapproximately 22.715 cm (8.943 inches).
 12. The driveshaft of claim 7,wherein the frusto-conical portion is arranged at approximately 14° withrespect to the axis.
 13. The driveshaft of claim 7 and furthercomprising: a hub pilot located adjacent to the forward face of theflange, wherein the hub pilot has a diameter of approximately 18.001 cm(7.090 inches), wherein a length of the tubular body, measured in anaxial direction, is approximately 22.715 cm (8.943 inches), wherein thefrusto-conical portion is arranged at approximately 14° with respect tothe axis, wherein the forward face of the flange is arranged atapproximately 2° with respect to the axis, wherein an outer diameter ofthe forward portion of the tubular body is approximately 7.117 cm (2.802inches), and wherein an inner diameter of the forward portion of thetubular body is approximately 4.994 cm (1.966 inches).
 14. A ram airturbine assembly for an aircraft, the assembly comprising: a turbinesubassembly having a rotatable hub; a gearbox positioned adjacent to thehub; a strut positioned adjacent to the gearbox, wherein the strutsupports the gearbox; a power conversion device; and a drivetrainoperably connected between the turbine subassembly and the powerconversion device, the drivetrain having a turbine driveshaft attachedto the hub and located at least partially within the gearbox, theturbine driveshaft including: a tubular body that defines an axis ofrotation and that includes a forward portion and a frusto-conicalportion located rearward of the forward portion; and a flange adjoiningthe forward portion of the tubular body opposite the frusto-conicalportion, the flange having a forward face and an opposite rear face,wherein a ratio of an outer diameter of the forward portion of thetubular body to an inner diameter of the forward portion of the tubularbody is in a range of approximately 1.423 to 1.425.
 15. A method ofinstalling a driveshaft in an aircraft ram air turbine, the methodcomprising: providing a driveshaft having a tubular body that includes aforward portion and a frusto-conical portion located rearward of theforward portion, and a flange adjoining the forward portion of thetubular body opposite the frusto-conical portion, the flange having aforward face and an opposite rear face, wherein a ratio of an outerdiameter of the forward portion of the tubular body to an inner diameterof the forward portion of the tubular body is in a range ofapproximately 1.423 to 1.425; positioning the driveshaft at leastpartially within a gearbox; and operatively engaging the driveshaft in adrivetrain that extends between a turbine and a power conversion device.